Question in Depth
I am trying to make a transmissive material that, when light passes through, the strength/intensity of the light is modified in some manner. The question is targeting the ability to modify light - specifically its strength, be it to increase/decrease the intensity of the light for all objects "behind" the transmissive object - solely after it passes through an object, rather than modifying the emitter.
My Considerations/Attempts
The Light Falloff node seems useful for emitters, but it seems relegated to use on emitters, not on an object that would later affect the light in some manner. The Light Paths node seems like it could be useful, perhaps utilizing the Transmission Ray to have it only affecting light passing through. But I've yet to determine how to utilize it to affect the light itself, rather than solely affecting the object's appearance (It is fun to utilize this to make "vampire" objects, though). The problem at its core seems to be figuring out how to modify the light [rays], rather than just the transmissive object.
My current best guess as to how to solve this would be to utilize a mix shader using transmission depth, then connecting an emitter that modifies the light. The problems then become having the emitter tied directly to all other light sources. Even assuming one light source, it would need to have access to the light's color and strength at the point of the transmissive object (maybe possible utilizing Light Falloff divided by Ray Length?), while also only emitting in the direction the light is coming from (or alternatively just being a "one-way" emitter, which may be possible utilizing normals). Regardless, I've been unable to make any of these guesses work. I'm hoping there's a nice, clean solution that I'm just not aware of.
Summary
I'm hoping to modify the light rays that pass through a transmissive object. The optimal solution would entail the following:
- Modify the strength of light.
- Modify the falloff of light.
- (Optional/Relevant) Modify the color of light.
Conclusion
Thus, the transmissive object is arguably not visually altered. Furthermore, the view of other objects through the transmissive object is not being targeted for alteration, but rather the light itself, which would cause both the view through the transmissive objects as well as the view around the transmissive object to be altered. Any solution need not necessarily target the light itself, but the results would optimally mimic the results that would be obtained from targeting the light itself.
Examples of desired capability:
- "night vision goggles" that amplify (increase the strength of) light that passes through them
- "welding mask" that reduce light that passes through it
- a "window" that causes the falloff through it to be cubic instead of the default quadratic (quadratic falloff divided by ray length should create cubic falloff)
(Potentially Relevant) Links
Can I only Render light that passes through an object?
Make light pass through solid object
Custom light falloff in Cycles
Point Light Strength in Cycles
Light Direction Vector Discussion
How the Light Path node works, with examples
Aside
If this question has been asked before, I welcome being pointed in the right direction, as I did not see any similar questions given in the site's provided suggestions when typing this question. Thank you in advance for whomever may have insight in this regard. (Finally, I'm not actually a complete novice to the site, this is just a new account for a new device, as I've forgotten the login info for my other device. So feel free to take the kid gloves off regarding any criticism. Though I may not be new, I'm likewise not an expert, so I've still lots to learn regarding the site's policies and culture)
Blender 2.92
